Self-propelled machines currently exist which can be equipped with a diagonally extending conveyor assembly in order that harvested crops are delivered to the inboard side of the path of cut taken by the machine, and, thus placed in a windrow alongside the standing crop yet to be cut. Then, on the next pass by the machine in the opposite direction, the same conveyor assembly delivers the severed material diagonally into a second windrow alongside the first, thereby providing double windrows for pickup by subsequent baling or other harvesting equipment. However, this type of double windrowing equipment is not designed for selective use; that is, the diagonal conveyor assembly is used continually throughout the harvesting procedure on every pass of the machine and requires that the machine go back and forth across the field instead of in a perimetricalmanner as is often preferred or necessary.